The present invention relates to a method for aligning two submerged pipe sections and to an apparatus for performing this method.
The technical field of the invention is that of methods and apparatus used for working under water.
Various methods and apparatus are known with respect to the alignment of pipes laid on the sea bed with a view to their joining together, particularly by welding in a gas pocket either by means of light-weight structures called "lifters" or by means of larger, heavier structures called "liners".
Said liners are placed on the bed and above the pipe and have handling and alignment means for picking up, raising and lining the pipe sections. Due to the fact that the deformations by bending the pipe are caused over short distances, the loads involved and the resulting stresses in the pipe are very considerable.
The use of such light-weight structures or lifters makes it possible to handle and align the submerged pipe sections, although such means do not always make it possible to achieve the desired precision.
Said lifters have already been used in combination with the liners in the following manner:
Two lifters are placed above the pipe, each at a relatively great distance from the welding point, approximately 20 to 30 meters in the case of conventional pipe dimensions and are manipulated so as to raise the pipe sections to the level of the welding zone, whereby said deformed sections are substantially horizontal to the bed and are at a distance therefrom which permits welding. A heavy metallic structure or liner is then brought above the ends of the pipe sections and is anchored to the sea bed. It grasps the pipe sections by means of clamps and aligns them. The loads involved are not as high as when the alignment is carried out with the liner alone, but are still significant, leading to excessive stressing of certain areas of the pipe.